In a large pot on medium-low heat, melt butter and add onion. Sauté until transparent (not brown) and then add asparagus. Let cook until soft, stirring occasionally (about five minutes).

Add flour and lemon juice and mix. Slowly stir in enough milk to fully cover the asparagus. Add salt and pepper, cover and let simmer for about 20 minutes, stirring occasionally. Cool slightly.

Blend until smooth using an immersion blender. (You might want to pour the soup through a sieve to catch any larger pieces, but I don’t find it necessary.)

Add heavy cream, and adjust seasonings. Garnish with chives and croutons and serve.

For the croutons, preheat toaster oven to 450 degrees Fahrenheit.

Brush melba toasts with olive oil.

Place about half a teaspoon of Parmesan cheese onto each piece of melba toast and bake for about three to four minutes. Serve on top of soup.